The present invention relates to hydraulic vane type pumps and, more particularly, to such pumps having under-vane pressure to assist vane extension.
Prior art power steering pumps have provided an exclusive flow path for the under-vane fluid in a vane type pump to improve cold priming. This exclusive flow path is from under the vanes in the pressure or discharge quadrant through a groove in the thrust plate to under the vanes in the inlet quadrant. The pressure plate has a groove in the inlet quadrant, which communicates the under-vane fluid in the inlet quadrant with the discharge flow of the pump. While this structure provides fast priming, it also induces high under-vane pressure when the system operating temperature is at the normal level, and the pump is operating within the normal speed range. This high under-vane pressure can induce early wear and reduces the overall life of the pump.
Further, in other prior art pumps, at particular operating conditions, the centrifugal force acting on the vanes is inadequate to insure the vane remains in contact with the internal contour of the pump ring. At all pump speeds, the pump outlet pressure in the high pressure area of the ring discharge is equal to the under-vane pressure which results in a floating vane condition at the ring contour. If a vane pump is operating at a relatively low speed, an external pressure can equalize or overcome the centrifugal force on the vanes and resulting under-vane pressure. This situation results in a reduced pumping efficiency along with noises from the floating vane condition.
Another prior art assembly disclosed in U.S. Pat. No. 4,386,891 to Riefel, et al discloses a rotary hydraulic vane pump with under-vane passage for assisting in priming. This assembly includes grooves in the thrust and pressure plates with the groove in the pressure plate being in communication with the discharge flow of the pump. The grooves incorporate restrictions to the under-vane fluid flow between the discharge and inlet positions of the vanes with the restriction in the thrust plate permitting more fluid flow than the restriction in the pressure plate to insure that most of the fluid will pass through the rotor under the vanes in the inlet to assist in vane extension. The grooves on the pressure plate are also isolated from one another in the direction of the low-to-high pressure transition.
The present invention provides a vane pump comprising a housing. The vane pump further comprises a rotating group including a ported thrust plate seated on the housing. The ported thrust plate includes a pair of thrust plate passageways thereon. The rotating group further includes a ported pressure plate having a pair of pressure plate passageways thereon. The rotating group also includes a cam ring disposed between the pressure plate and the thrust plate. The vane pump further comprises an oval-shaped wall on the cam ring cooperating with the pressure plate and the thrust plate to define a rotor chamber in the rotating group.
The vane pump further comprises a rotor supported in the rotor chamber for rotation about a longitudinal axis of the vane pump. The vane pump further includes a plurality of radial vane slots in the rotor. Each of the vane slots defines an under-vane cavity. The thrust plate passageways and the pressure plate passageways are axially aligned with the under-vane cavities. The vane pump further comprises a plurality of flat vanes slideable in respective ones of said vane slots. Each of the thrust plate passageways includes two generally kidney-shaped passages joined by a restricted passage. Each of the thrust plate passageways is isolated from fluid communication with the next adjacent thrust plate passage.
It is, therefore, an object of the present invention to provide an under-vane pump separating the low-to-high pressure regions of the vane pump. This is accomplished by closing the low-to-high pressure transition in the thrust plate.